The present invention relates to a technique that minimizes a time period required for raising internal temperature of fuel cells to a stationary level (that is, a preset temperature capable of generating a required output) at the time of activating the fuel cells.
Fuel cells, which receive a supply of gaseous fuel and generate electric power, have a high energy efficiency and are thereby promising as a power source of electric vehicles. In the case where the fuel cells are used as the power source of an electric vehicle, a motor is driven with the electric power generated by the fuel cells and outputs a torque, which is transmitted to an axle to give a propulsive force of the electric vehicle. The following problem, however, arises when the fuel cells are used as the power source of an electric vehicle.
The fuel cells having low internal temperature do not generate a sufficient output to fulfill a required output of the electric vehicle. It is accordingly required to raise the internal temperature of the fuel cells to the stationary level when the fuel cells are used as the power source of the electric vehicle. At the time of starting the electric vehicle, that is, at the time of activating the fuel cells, the fuel cells have low internal temperature. It accordingly takes a relatively long time to raise the internal temperature of the fuel cells to the stationary level with the Joule heat generated through electrochemical reactions.
In order to solve such a problem, the prior art technique, for example, as disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 58-23167, drives the motor by means of a secondary battery, which is connected in parallel with the fuel cells, at the time of activating the fuel cells, cools down the motor with the air, and feeds the warm air, which has been heated through the motor-cooling process, to the fuel cells to raise the internal temperature of the fuel cells to the stationary level in a shorter time period.
Since a rotor and a stator included in the motor have large heat capacities, the temperature of the motor does not rise to a high level immediately after the start of the motor. The air that is used to cool down the motor and then fed to the fuel cells accordingly does not have a sufficiently high temperature at the time of starting the motor. This proposed technique thus requires some time to raise the internal temperature of the fuel cells to the stationary level at the time of activating the fuel cells.
The object of the present invention is thus to solve the problems arising in the prior art techniques and to provide a fuel cells system that is capable of raising internal temperature of fuel cells to a stationary level in a shortest possible time at the time of activating the fuel cells, as well as a method of controlling actuation of such a fuel cells system.
At least part of the above and the other related objects is attained by a first fuel cells system of the present invention including fuel cells that receive a supply of gaseous fuel and generate electric power.
The first fuel cells system includes: a motor that is driven with the electric power output from the fuel cells; and a motor control unit that controls drive of the motor. The motor control unit controls the drive of the motor, in order to cause the motor to consume the electric power output from the fuel cells without producing any torque at a drive shaft of the motor at the time of activating the fuel cells.
The present invention is also directed to a first method of controlling actuation of a fuel cells system, which includes: fuel cells that receive a supply of gaseous fuel and generate electric power; and a motor that is driven with the electric power output from the fuel cells.
The first method includes the steps of:
(a) controlling activation of the fuel cells;
(b) controlling drive of the motor, in order to cause the motor to consume the electric power output from the fuel cells without producing any torque at a drive shaft of the motor at the time of activating the fuel cells.
The first fuel cells system of the present invention and the corresponding first method of controlling actuation of the fuel cells system control drive of the motor, in order to cause the motor to consume electric power output from the fuel cells without producing any torque at the drive shaft of the motor.
In the first fuel cells system of the present invention and the corresponding first method of controlling actuation of the fuel cells system, at the time of activating the fuel cells, the motor is controlled to consume the electric power output from the fuel cells at the time of activating the fuel cells. This arrangement causes the electric power to be forcibly drawn from the fuel cells and thereby enhances the electrochemical reactions proceeding in the fuel cells. The enhanced reactions increase the Joule heat and enable the internal temperature of the fuel cells to be raised to the stationary level in a short time period. While the motor consumes the electric power, no torque is produced at the drive shaft of the motor. Namely the motor is not practically actuated under the condition of an insufficient output of the fuel cells. For example, in the case where the fuel cells system is mounted on the electric vehicle, the electric vehicle is not driven while the output of the fuel cells is not sufficient for the required output of the electric vehicle.
In accordance with one preferable application of the present invention, the first fuel cells system further includes a temperature detection unit that measures internal temperature of the fuel cells. The motor control unit controls the drive of the motor to vary the electric power consumed by the motor according to the observed internal temperature.
The arrangement of varying the electric power drawn out of the fuel cells according to the observed internal temperature of the fuel cells enables the internal temperature of the fuel cells to be raised to the stationary level at a high efficiency in a shorter time period without exceeding the allowable range of the electric power produced by the fuel cells.
In accordance with another preferable application of the present invention, the first fuel cells system further includes: a secondary battery that is capable of supplying electric power to the motor, in order to drive the motor; and a battery supply regulation unit that regulates a supply of electric power from the secondary battery to the motor. The battery supply regulation unit cuts off the supply of electric power from the secondary battery to the motor at the time of activating the fuel cells.
In the structure including the secondary battery, cutting off the supply of electric power from the secondary battery to the motor increases the rate of consumption of the electric power from the fuel cells by the motor and thereby the electric power drawn out of the fuel cells, thus enabling the internal temperature of the fuel cells to be raised to the stationary level in a shorter time period.
In accordance with one preferable embodiment of the first fuel cells system, the motor control unit controls the drive of the motor, which is expressed as a d-q axes model, to make a value of electric current flowing through a q-axis winding substantially equal to zero and a value of electric current flowing through a d-axis winding equal to a predetermined value of not less than zero.
Such control causes the motor to consume the electric power through the ohmic loss of the d-axis winding without producing any torque at the drive shaft.
In the embodiment of controlling drive of the motor in the above manner, the first fuel cells system further includes a temperature detection unit that measures internal temperature of the fuel cells. The motor control unit controls the drive of the motor to vary the value of electric current flowing through the d-axis winding according to the observed internal temperature.
This arrangement varies the value of electric current flowing through the d-axis winding according to the internal temperature of the fuel cells to vary the electric power consumed by the motor, thus enabling the internal temperature of the fuel cells to be raised to the stationary level at a high efficiency in a shorter time period.
In accordance with still another preferable application of the present invention, the first fuel cells system further includes: a gaseous fuel generation unit that produces the gaseous fuel from a supply of crude fuel and feeds the produced gaseous fuel of a relatively high temperature to the fuel cells; and a flow regulation unit that regulates a flow rate of the gaseous fuel of the relatively high temperature fed from the gaseous fuel generation unit to the fuel cells. The flow regulation unit increases the flow rate of the gaseous fuel of the relatively high temperature to be greater than a predetermined standard flow rate at the time of activating the fuel cells.
The gaseous fuel fed from the gaseous fuel generation unit generally has a relatively high temperature. Increasing the flow rate of the gaseous fuel supplied from the gaseous fuel generation unit to the fuel cells enables the internal temperature of the fuel cells to be raised to the stationary level in a further shorter time period.
The present invention is also directed to a second fuel cells system having fuel cells that receive a supply of gaseous fuel and generate electric power. The fuel cells system includes: a gaseous fuel generation unit that produces the gaseous fuel from a supply of crude fuel and feeds the produced gaseous fuel of a relatively high temperature to the fuel cells; and a flow regulation unit that regulates a flow rate of the gaseous fuel of the relatively high temperature fed from the gaseous fuel generation unit to the fuel cells. The flow regulation unit increases the flow rate of the gaseous fuel of the relatively high temperature to be greater than a predetermined standard flow rate at the time of activating the fuel cells.
The present invention is further directed to a second method of controlling actuation of a fuel cells system, which includes fuel cells that receive a supply of gaseous fuel and generate electric power, a gaseous fuel generation unit that produces the gaseous fuel from a supply of crude fuel and feeds the produced gaseous fuel of a relatively high temperature to the fuel cells, and a flow regulation unit that regulates a flow rate of the gaseous fuel of the relatively high temperature fed from the gaseous fuel generation unit to the fuel cells.
The second method includes the steps of:
(a) controlling the gaseous fuel generation unit and activation of the fuel cells; and
(b) increasing the flow rate of the gaseous fuel of the relatively high temperature to be greater than a predetermined standard flow rate at the time of activating the fuel cells.
The second fuel cells system of the present invention and the corresponding second method of controlling actuation of the fuel cells system increase the flow rate of the gaseous fuel of the relatively high temperature fed from the gaseous fuel generation unit to the fuel cells to be greater than the predetermined standard flow rate at the time of activating the fuel cells.
The gaseous fuel fed from the gaseous fuel generation unit has a relatively high temperature. In the second fuel cells system and the corresponding second method of controlling actuation of the fuel cells system, increasing the flow rate of the gaseous fuel fed from the gaseous fuel generation unit to the fuel cells at the time of activating the fuel cells thus enables the internal temperature of the fuel cells to be raised to the stationary level in a short time period.
In the configuration of regulating the flow rate of the gaseous fuel in the above manner, it is preferable that the second fuel cells system further includes a temperature detection unit that measures internal temperature of the fuel cells and that the flow regulation unit returns the flow rate of the gaseous fuel to the predetermined standard flow rate when the observed internal temperature reaches a preset level.
The arrangement of returning the flow rate of the gaseous fuel to the predetermined standard flow rate when the internal temperature of the fuel cells reaches the stationary level effectively prevents a wasteful, unnecessary supply of the gaseous fuel to the fuel cells.
In accordance with one preferable application of the present invention, the second fuel cells system further includes a gaseous exhaust flow conduit that introduces an exhaust of the gaseous fuel discharged from the fuel cells into the gaseous fuel generation unit. The gaseous fuel generation unit attains combustion of the introduced gaseous exhaust to obtain part of thermal energy required to produce the gaseous fuel.
As described above, the increased flow rate of the gaseous fuel fed to the fuel cells at the time of activating the fuel cells may increase the quantity of the gaseous fuel that does not contribute to the power generation in the fuel cells. This application causes the non-contributing portion of the gaseous fuel to be effectively used as the gaseous exhaust by the gaseous fuel generation unit, thus preventing the waste of the gaseous fuel.
The present invention is also directed to a first electric vehicle with a fuel cells system mounted thereon. Here the fuel cells system includes: fuel cells that receive a supply of gaseous fuel and generate electric power; a motor that is driven with the electric power output from the fuel cells; and a motor control unit that controls drive of the motor.
In the first electric vehicle, a torque produced at a drive shaft of the motor is transmitted to an axle to give a propulsive force of the electric vehicle. The motor control unit controls the drive of the motor, in order to cause the motor to consume the electric power output from the fuel cells without producing any torque at the drive shaft of the motor at the time of activating the fuel cells.
The present invention is further directed to a second electric vehicle with a fuel cells system mounted thereon. Here the fuel cells system includes: fuel cells that receive a supply of gaseous fuel and generate electric power; a gaseous fuel generation unit that produces the gaseous fuel from a supply of crude fuel and feeds the produced gaseous fuel of a relatively high temperature to the fuel cells; and a flow regulation unit that regulates a flow rate of the gaseous fuel of the relatively high temperature fed from the gaseous fuel generation unit to the fuel cells.
In the second electric vehicle, a torque produced at a drive shaft of a motor is transmitted to an axle to give a propulsive force of the electric vehicle. The flow regulation unit increases the flow rate of the gaseous fuel of the relatively high temperature to be greater than a predetermined standard flow rate at the time of activating the fuel cells.
The first electric vehicle and the second electric vehicle of the present invention respectively have the above-specified fuel cells systems mounted thereon. These arrangements enable the internal temperature of the fuel cells to be raised to the stationary level in a short time period at the time of starting the electric vehicle. The electric vehicle thus quickly starts driving with the fuel cells in the stationary state.